Anthropic replaces Git with custom Scion source control system
Key Takeaway
Anthropic built a custom source control system called Scion to handle massive scale, managing over 30,000 daily merges and 25 million daily checkouts.
Summary
Due to a massive increase in code change velocity, Anthropic has migrated from Git to a custom-built source control system named Scion. The move was driven by extreme scale requirements, including a 100 GB main branch history and the need to avoid massive Git traffic overhead. The new system includes a code review component called Antique and was developed by a seven-person team over five months.
Technical scale of Scion
- Scale requirements: The main branch history is nearly 100 GB, with a compressed working copy exceeding 25 GB.
- Throughput: The system handles approximately 25 million code checkouts per day for CI, developer environments, and agent sandboxes.
- Architecture: Scion utilizes a "derived data" concept inspired by Meta's Sapling (Mononoke) and Google's Piper.
- Connectivity: The system lacks offline support because its primary user, the Claude AI, is always online.
- Review system: A new code review system named Antique is used alongside Scion.
Why it matters
This demonstrates how extreme AI-driven development velocity can outpace the performance capabilities of standard distributed version control systems like Git.
Original reference: simonwillison.net →